Some types of image sensors are semiconductor devices that convert an optical image into an electrical signal. Examples of semiconductor image sensors are charge-coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) image sensors.
When manufacturing some types of image sensors, transistors and photodiodes may be formed in a semiconductor substrate and may be electrically connected. An insulating layer structure and lines may be formed on and/or over the transistors and the photodiodes. While the lines are formed, a pad may be formed that is connected to the transistor. The pad may be connected to a conductive wire. The pad may be exposed from the insulating layer structure to electrically connect the pad to the conductive wire. At least one color filter (e.g. including red, green, and blue colors) may be formed on and/or over the insulating layer structure. An overcoat layer may then be formed on and/or over the color filter. A photoresist film may be formed on and/or over the overcoat layer. A reflow process may be performed to form microlenses that are used to condense light onto the photodiodes.
However, during formation of a color filter and/or microlens, a pad of the image sensor may be exposed from the insulating layer structure. Accordingly, the surface of the pad may be oxidized during formation of a color filter and microlens, resulting in a contact between the pad and the conductive wire being weakened.